A projection display is capable of converting light from a light source into an optical image in accordance with an image signal using a display device and projecting the optical image on a screen enlargedly by means of a projection lens, thereby providing a large-scale image. There are various types of projection displays, one of which is a rear projection display for projecting an image from the rear face of a projection screen.
Projection displays, however, have the drawback of creating a vertical and horizontal trapezoidal distortion in a projected image depending on the positional relationship between the screen and projector. Further, many projection displays have an optical component such as a mirror on an optical path from the projector to the screen, which creates a distortion of a display image depending on the optical characteristics of the optical component. Such distortion resulting from the optical characteristics of the optical component has a complicated shape containing a quadratic or higher order component, rather than a vertical and horizontal trapezoidal shape.
To solve the above-described problems, a projection display capable of correcting for a distortion created in a display image is required. A projection display having such function is provided with reflection members on the four corners of the screen for displaying an image and detecting the intensity of reflected light from the reflection members by an optical sensor to obtain positional information of the four reflection members, thereby automatically correcting for a vertical and horizontal trapezoidal distortion of a display image (cf. Japanese Patent Application Laid-Open No. 2006-186469). There is another type of projection display of automatically detecting the position of the screen edge, capturing a plurality of adjusting points displayed on the screen with a camera, calculating a displacement of each adjusting point displayed on the screen from a predetermined reference point by image processing, and correcting for a distortion of a display image on the basis of the result of calculation (cf. Japanese Patent Application Laid-Open No. 8-88860 (1996)).
However, the projection display described in the above-mentioned JP2006-186469 is capable of correcting for a vertical and horizontal trapezoidal distortion using positional information of the reflection members disposed on the four corners of the screen, but incapable of correcting for a distortion resulting from the optical characteristics of the optical component provided for the display. Further, it is difficult in a rear projection display to detect reflected light from reflection members.
A projector described in the above-mentioned JP8-88860 is limited to a CRT projector, and when capturing an image of the screen with a camera built in the rear projection display, it is difficult to detect the screen by image processing due to the presence of structural members such as a frame for fixing the screen, and an image processor is accordingly required.